1. Field of the Invention
The present invention relates to electrostatographic imaging and recording apparatus, and particularly to surface contacting members for toner fixing assemblies in these apparatus.
2. Description of Background and Other Information
Generally in electrostatographic reproduction, the original to be copied is rendered in the form of a latent electrostatic image on a photosensitive member. This latent image is made visible by the application of electrically charged toner.
The toner thusly forming the image is transferred to a substrate, such as paper or transparent film, and fixed or fused to the substrate. The fusing of toner to substrate can be effected by applying heat, preferably at a temperature of about 90° C.-200° C.; pressure may be employed in conjunction with the heat.
A system or assembly for providing the requisite heat and pressure customarily includes a fuser member and a support member. The heat energy employed in the fusing process generally is transmitted to toner on the substrate by the fuser member. Specifically, the fuser member is heated; to transfer heat energy to toner situated on a surface of the substrate, the fuser member contacts this toner, and correspondingly also can contact this surface of the substrate itself. The support member contacts an opposing surface of the substrate. Accordingly, the substrate can be situated between the fuser and support members, so that these members can act together on the substrate to provide the requisite pressure in the fusing process.
During the fusing process toner can be offset from the substrate to the fuser member. Toner thusly transferred to the fuser member in turn may be passed on to other members in the electrostatographic apparatus, or to subsequent substrates subjected to fusing.
Toner on the fusing member therefore can interfere with the operation of the electrostatographic apparatus and with the quality of the ultimate product of the electrostatographic process. This offset toner is accordingly regarded as contamination of the fuser member, and preventing or at least minimizing this contamination is a desirable objective.
Release agents, such as those comprising polydimethylsiloxanes, can be applied to fusing members during the fusing process, to combat toner offset. However, these agents may interact with the fusing member surface upon repeated use, and in time cause swelling, softening, and degradation of the fuser member.
Other factors also may disadvantageously affect the fusing member. Heat energy applied to this member can cause its degradation. Degradation can also be effected by continual contact with substrate toner, and by toner remaining on the fusing member surface. The fusing member surface can be subjected to abrasion by a variety of sources—such as the substrate, for instance, as well as elements of the fusing system, like the support member, release agent applicator, and contact heating members, if these are employed.
These unfavorable effects can result in an uneven fusing member surface and defective patterns in thermally fixed images. Where the substrate employed is paper, abrasion of the fusing member surface at the paper edge can form a worn area, or groove, that becomes problematic when the paper size is changed so that a larger paper overlaps the worn area. When the groove becomes deep enough to affect the fixing of the toner it causes objectionable image defects.
Where high image quality, and/or high image gloss, and/or controlling fusing member surface roughness are required, surface wear and abrasion are particular problems. For instance, if obtaining very high image quality is the objective, even a groove only worn into the surface enough to show a variation in surface gloss will nevertheless generate an objectionable defect in the image.
Inorganic fillers have been incorporated into fluoroelastomer surface layers to achieve the desired combination of properties like wear resistance, modulus, and thermal conductivity. However, it is difficult to provide surface layers which are suitably free of defects, and which—in combination with high wear resistance—have a sufficiently high gloss, or are otherwise of the requisite degree of smoothness. Particularly it is difficult to provide surface layers with these desirable properties where the layers are obtained by application of the fluoroelastomer composition in solution, especially where the layers are built up to the desired thickness by applying successive coats.
U.S. Pat. No. 4,064,313 discloses a fuser member with an intermediate polysiloxane layer, for adhering a silicone rubber outer layer to the fuser core. This patent further teaches including finely powdered silica in the polysiloxane material, to improve mechanical strength. U.S. Pat. No. 4,199,626 discloses including silica as a filler in the fluoropolymer surface layer of a fuser member.
However, silica incorporated in fluoroelastomer compositions renders the compositions more difficult to dissolve. This difficulty interferes with using these compositions to make the coating preparations from which fuser member layers are formed.
The incorporated silica also causes crepe hardening in the fluoroelastomer compositions, leading them to exhibit very poor coating qualities. Specifically, the crepe hardening results in gel defects in the coating preparations, and ultimately in fuser member layers formed from these preparations. These defects bring roughness to the fuser member surfaces, and diminish gloss.